A micro-fluid ejection device, such as a thermal ink jet printer, may be used to form an image on a printing surface by ejecting small droplets of ink from an array of nozzles on an ink jet printhead as the printhead traverses the print medium. The fluid droplets may be expelled from a micro-fluid ejection head when a pulse of electrical current flows through the fluid ejection actuator on the ejection head. When the fluid ejection actuator is a resistive fluid ejection actuator, vaporization of a small portion of the fluid creates a rapid pressure increase that expels a droplet(s) of fluid from a nozzle, such as one positioned over the resistive fluid ejection actuator. Typically, there is one resistive fluid ejection actuator corresponding to each nozzle of a nozzle array on the ejection head. Conventionally, the resistive fluid ejection actuators are activated under the control of a microprocessor in the controller of the micro-fluid ejection device.
Resistive fluid ejection actuators are prone to mechanical damage from cavitation as the gas bubble collapses after droplet ejection. Any non planar topography adjacent to the actuator pad, particularly at the edges of the pad where conductor lines terminate, may act as a stress riser for conformal overcoats or films that are applied to protect the actuator pad. Non-planar topographies may also cause non-homogenities in the overcoats or films. Such non-homogenities may also result from the thermal gradient between the relatively hot center of the actuator pad and the relatively cool edges.
With reference to FIG. 1, there is shown a conventional heater structure 10 for a resistive fluid ejection actuator, in the form of a resistive heater, for a micro-fluid ejection head. In this structure 10, there is provided a substrate 12 containing a thermal barrier layer 14 having a resistive layer 16 deposited thereon. The resistive layer 16 is in electrical contact with a conductor layer 18. The conductor layer 18 is etched or otherwise configured to provide a heater pad area 20 between conductive portions 18A and 18B. As the conductor layer 18 is relatively thick (e.g., about 5000 Angstroms), a subsequent dielectric layer 22 and cavitation layer 24 must step up at edges of the heater pad area 20 to cover and seal exposed portions of the conductive portions 18A and 18B to prevent corrosion of the conductive portions 18A and 18B. Additional layers, such as an insulating layer 26 and a passivation layer 28 are conventionally included to complete the heater structure 10.
The mechanical, cavitational, thermal, and other stresses associated with the conventional non-planar heater structure 10 may collectively result in weak areas in the film or overcoat layers 22-28 that are prone to fracture, causing pre-mature failure of the actuator. For example, the step up areas represent high stress regions S. As the overcoats layers 22-28 become thinner in an effort to increase a thermal efficiency of the heater structure 10, the likelihood of weak or highly stressed areas in the layers 22-28 increases.
Therefore, the present inventors appreciated that a need exists for avoiding non-planar topographies in the manufacture of micro-fluid ejection devices of the type having resistive fluid ejection actuators. In addition, the present inventors appreciated that a need exists for providing such actuators having improved thermal efficiency.
The foregoing and other needs may be provided by a substantially planar fluid ejection actuator and methods for manufacturing substantially planar fluid ejection actuators for micro-fluid ejection heads. One such fluid ejection actuator includes a conductive layer adjacent to a substrate that is configured to define an anode segment spaced apart from a cathode segment. A thermal barrier segment is disposed between the anode segment, cathode segment, and thermal barrier segment. A resistive layer is applied adjacent to the substantially planar surface. The actuator is particularly suitable for use as a fluid ejection head, such as a micro-fluid ejection head.
In another aspect, an exemplary embodiment of the disclosure provides a method for manufacturing a substantially planar resistive fluid ejection actuator. According to the method, a conductive layer adjacent to a support substrate is configured to have an anode segment spaced apart from a cathode segment with a well therebetween. A thermal barrier layer is applied within the well and over the anode segment and cathode segment. At least a portion of the thermal barrier layer is removed to expose the anode segment and cathode segment and to define a thermal barrier segment within the well. A substantially planar surface is provided by the anode segment, cathode segment, and the thermal barrier segment. A resistive layer is applied adjacent to the planar surface to provide a fluid ejection actuator.
The embodiments described herein improve upon the prior art in a number of respects. The disclosed embodiment may be useful for a variety of applications in the field of micro-fluid ejection devices, and particularly with regard to inkjet printheads having improved longevity and less susceptibility to mechanical failure.
Another advantage of the embodiments described herein is that thinner protective layers may be used that may be effective to increase the energy efficiency of the fluid ejector actuators.